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Getting the Champions League title is not as easy as other domestic leagues, the Champions League is a collection of great teams all over Europe so it will not be easy for Barcelona to achieve that dream even though they have brought their team to a great performance.
The Champions League has a different sensation and the mentality of coaches and players is still influential if they do not have deep experience in the UCL, I believe Barcelona this time will be better to go to UCL even though the previous season could only stop at the group stage.
You are of course right there especially about the Champions League competition. All the participants who qualify for the group stages are the best teams in Europe from their respective leagues and of course they also hope to impress and win something.
Barcelona need time to win the Champions League title, but maybe Xavi can make it happen if he really has players who can play well every game. Luck also plays an important role in his quest for the title, but team performance is a good yardstick for determining probabilities.